Liquid crystal displays (LCDs) have been prevailing in the market of flat display devices because they are light, thin and of low power consumption. Especially, thin film transistor liquid crystal displays (TFT-LCDs) are the currently popular type of LCDs.
LCDs depend on the light transmission characteristic of liquid crystal to display images and need an external light source because liquid crystal does not emit light by itself. According to the type of the external light source, LCDs can be classified into a transmissive type, a reflective type, and a transreflective type. Transmissive LCDs comprise a backlight under an array substrate, and the light for the liquid crystal is provided by the backlight. Reflective LCDs comprise a reflective part instead of a backlight, and the light from the external environment is reflected by the reflective part through the liquid crystal to display images. Transreflective LCDs can be deemed as the combination of the above two types of LCDs and have transmissive regions and reflective regions. Transreflective LCDs use a backlight as a light source for the transmissive regions to avoid depending on environment light, and on the other hand, they also can reflect environment light with a reflective part in the reflective regions and save power consumption, thus transreflective LCDs have the functions of both transmission and reflection of light.
In order to enhance the view angle scope of a LCD, generally a reflective part is provided on the whole array substrate in the transreflective liquid crystal display. That the reflective part is formed on the whole array substrate influences the processing such as photolithograph process and etching process on the other layers formed on the substrate. In order to cope with this problem, a method is proposed in which projections are formed with a resin material on the substrate, and then a metal film is deposited on the resin projections so as to form a reflective part. Light diffuse reflection can occur on thus formed reflective part to supply light for liquid crystal.
FIG. 1 is a sectional view of an array substrate in a conventional transreflective LCD. The array substrate comprises a substrate 1, a gate scanning line and a data line that are formed on the substrate 1, and a thin film transistor 20 comprising a gate electrode 2, an active layer 8, a source electrode 5, and a drain electrode 6. An insulating layer 3 made of silicon nitride (SiNx) is disposed between the gate electrode and the active layer as a gate dielectric layer, the thin film transistor 20 and the data line 2 are covered by a passivation layer 9, and a pixel electrode 10 is formed on a portion of the passivation layer 9 other than that corresponding to the thin film transistor 20. The pixel electrode 10 comprises a transmissive region 30 and a reflective region 40, and is connected with the drain electrode 6 through a passivation through hole 7. Generally, the reflective part is formed with resin projections 14 and a metal film 13 provided on the resin projections, and the reflective part can be formed on the pixel electrode, under the pixel electrode 10, or in the same layer as the pixel electrode 10. Light diffuse reflection can occur when light is irradiated on the metal film 13 so as to supply the reflected light for the liquid crystal between the array substrate and a color filter substrate facing the array substrate. In order to fabricate the array substrate of the above configuration, the patterning process comprising photolithography and etching with a mask is used to form the layer structure. One exemplary method for the patterning process comprises the following steps: depositing a desired material for the layer to be fabricated; applying a photoresist film on the layer; exposing with a mask; developing the exposed photoresist film to form a photoresist pattern; etching the layer with the photoresist pattern as an etching mask; removing the residual photoresist pattern so that the layer is patterned as required. Besides the above method for fabricating the resin projections 14, SiNx can be used to form the projections so as to avoid the problem that the resin material can not be processed at a high temperature and to improve the processing ability at a low temperature.
However, there are the following problems in the conventional method. The size of the projections formed by the resin materials is relatively large, which increases the thickness of the final product, so that the use of photolithography process is highly limited. Since a patterning process is performed on the resin materials, the processes of masking, exposing, and etching are increased by 2-3 times. The effect of the light diffuse reflection is not very good, because it is dependent on the thickness of the projections and the size of the trenches between the projections. The resin projections formed by patterning resin material normally have a relatively large size and a relatively large gap, thus the reflectivity is uniformed across the substrate and the poor light diffuse reflection leads to a limited emitting angle range of the reflected light. Therefore, for the array substrate fabricated by the above conventional method, the effect of the light diffuse reflection is not desirable. Moreover, the manufacturing procedure is complicated and the yield is low. Also, the quality of the final product is decreased and the cost is increased.